The role of tropical cyclones in cross-equatorial total energy transports

An important focus of ongoing research in tropical meteorology is why there are, on average, 60 tropical cyclones (TCs) in the Northern Hemisphere (NH) annually and how this number may vary in response to climate change. One potential explanation for the average annual frequency of NH TCs is that TCs have a significant aggregate annual role in transporting energy out of the tropics during boreal summer and fall. While the contribution of TCs to aggregate annual atmospheric energy transports remains uncertain, recent research has suggested that TCs may play a significant role in atmospheric meridional heat transports given the strong correlation between aggregate TC activity and meridional heat transports during the following winter. Building upon prior work, the present study seeks to advance our understanding of the potential role of TCs in aggregate transports of atmospheric energy by quantifying whether the upper-tropospheric outflow of TCs is responsible for transporting significant quantities of total energy (i.e., sum of kinetic energy, latent energy, potential energy, and sensible heat) in the upper troposphere from the NH tropics into the Southern Hemisphere (SH) tropics during the peak of NH TC season.

The current study utilizes storm-relative composites of vertically integrated meridional total energy transports computed from the NCEP Climate Forecast System Reanalysis and the ECMWF Interim Re-Analysis for eastern North Pacific, western North Pacific (WPAC), and North Atlantic TCs to quantify the contribution of these TCs to cross-equatorial total energy transports. Results for the composites of WPAC TCs reveals that the upper-tropospheric outflow jet of the TC is responsible for significant cross-hemispheric total energy transports. Zonal integration of the composited meridional total energy transports over a 5000 km distance reveals more than a doubling of southward total energy transports at the equator relative to climatology. The southward upper-tropospheric total energy transports by the TC primarily consist of dry static energy transports (i.e., sum of potential energy and sensible heat) and are much stronger than the northward lower-and-midtropospheric transports of moist static energy (i.e., sum of latent energy, potential energy, and sensible heat) by the TC. The meridional dry static energy transports from the NH to the SH by WPAC TCs in the deep tropics suggests that these TCs may serve to temporarily increase the meridional transport of dry static energy from the NH to the SH that typically occurs in the WPAC during boreal summer and fall. The large-scale atmospheric environment directly to the east and west of the TC exhibits anomalous northward transports of total energy at the equator, which largely cancel out the anomalous southward energy transports by the TCs. This compensation in meridional energy transports between the TC and its surrounding environment is a topic of ongoing research.